1. Field of the Invention
The present invention relates to a self-cleaning filter, particularly for feed waters in industrial plants. More specifically this filter is above all adapted to be used in cooling plants fed in with sea water.
It is known that many industries need the presence of cooling plants having an important water delivery in order to allow the correct operation of the corresponding production plants.
Due to obvious economical reasons, it often appears convenient to use water directly drawn from natural sources as a cooling fluid for said plants. In other words the feed water is directly drawn for example from a river, then it is passed through the plant and finally it is discharged into the river again. But the feed water thus obtained contains a number of suspending elements (mould, deposits or the like) which, if introduced into the cooling plant, could in a short time cause a remarkable decreasing in the effectiveness of the same. Thus the water is conveniently filtered before being introduced into the plant, by means of appropriate filters disposed upstream of the plant itself.
2. Prior Art
In this field of the industry many types of filters are already known and normally used; they are different from one another under many parameters such as for example the shape and arrangement of the filtering elements or the adopted filtering method.
One of said filters which is important to the ends of the present invention, carries out filtration letting the feed water pass through a number of filtering elements that are automatically cleaned when necessary through appropriate means.
More particularly, said filter comprises a cylindrical body within which a central plate provided with a series of through holes is fastened. The central plate defines an inlet chamber and an outlet chamber in said cylindrical body. When the feed water goes from the inlet to the outlet chamber it is obliged to pass through filtering elements which retain the solid particles suspended therein.
Each of said filtering elements substantially consists of a tubular body closed at one end, provided over the whole surface thereof with a plurality of calibrated holes.
Filtering elements of this type are commonly known in the sector under the name of "filtering candles".
Each filtering element is sealingly engaged at its open end with one of the through holes provided on the central plate. In the region of their respective closed ends said filtering elements are fastened to a support plate by means of screw threaded elements. The support plate, in turn, is rigidly connected to the central plate through a series of stud rods adapted to be screwed down into the latter and connected to the support plate itself through screw threaded elements.
Provision is also made for regeneration means adapted to restore the effectiveness of the filtering elements when the storing up of the material retained in the same inhibits water from passing therethrough.
Such regeneration means consists of cleaning tubes inside which the vacuum is created by a suction pump connected thereto. The cleaning tubes, moved by suitable devices, pass close to the open ends of the filtering elements and suck the material stored therein.
It is also provided that the regeneration means is automatically operated upon command of a differential pressure switch actuating it when the pressure gradient between the inlet chamber and the outlet chamber exceeds a predetermined limit value.
Although the filter briefly described hereinbefore has proved to be quite effective and of practical use under many situations, it is not very reliable when, as it often happens, it must be used to filter sea water or anyway water containing corrosive substances.
Such a drawback is due to the action of the corrosive agents present in the water, which very easily wear away the screw threaded connections causing, after a certain lapse of time, the separation between the corresponding members.
It is apparent that under this situation the removal of one or more of said filtering elements from their housings may occur or even the simultaneous removal of all said elements due to the detachment of the support plate from the central plate.
In both cases the above drawback will give rise, on one hand, to the ineffectiveness of the filter due to the fact that the water can freely pass from the inlet chamber to the outlet chamber without being filtered and, on the other hand, to the introduction of a plurality of fragments and metal particles into the plant. Obviously, in this case the cooling plant would be greatly damaged and the repairs would involve rather important expenses.
In order to avoid the occurrence of said damages it appears therefore necessary to replace the filtering elements and the respective plates prematurely, when they could still be used for a long time.
Said inconvenience is further made worse by the fact that, always due to said connections by means of threaded elements, the above described operation appears very long, difficult and hard.